zoukankan      html  css  js  c++  java
  • Leetcode: 91. Decode Ways

    Description

    A message containing letters from A-Z is being encoded to numbers using the following mapping:

    'A' -> 1
    'B' -> 2
    ...
    'Z' -> 26
    

    Given an encoded message containing digits, determine the total number of ways to decode it.

    Example

    Given encoded message "12", it could be decoded as "AB" (1 2) or "L" (12).
    
    The number of ways decoding "12" is 2.
    

    思路

    • 动态规划
    • 对每个数组首先判断其是否为0,若是将改为dp赋0,若不是,赋上一个dp值,此时相当如加上了dp[i - 1], 然后看数组前一位是否存在,如果存在且满足前一位不是0,且和当前为一起组成的两位数不大于26,则当前dp值加上dp[i - 2],

    代码

    class Solution {
    public:
        int numDecodings(string s) {
            int len = s.size();
            if(len == 0) return 0;
            
            vector<int> dp(len + 1, 0);
            dp[0] = 1;
            
            
            for(int i = 1; i < len + 1; ++i){
                dp[i] = (s[i - 1] == '0') ? 0 : dp[i - 1];
                
                if(i > 1 && (s[i - 2] == '1' || (s[i - 2] == '2' && s[i - 1] <= '6')))
                    dp[i] += dp[i - 2];
            }
            
            return dp[len];
        }
    };
    
  • 相关阅读:
    作业16
    递归函数
    三元表达式与生成式
    迭代器与生成器
    作业15
    装饰器
    作业14
    string的入门与进阶
    修理牧场(优先队列)
    旅游规划
  • 原文地址:https://www.cnblogs.com/lengender-12/p/7058393.html
Copyright © 2011-2022 走看看